Welcome to the forum.
As you probably know the earlier models were built in much smaller numbers than the later J&J designs. The 390 was one of the last designs from Axel Mohnhaupt before the change to J&J. In some ways it was a sort of transition design between earlier heavier types being aimed (particularly the Caribic model you are looking at) at the growing charter market then dominated by French builders. If you look at the data on Sailboatdata for the different models you will find a lot of similarities to the later 40'designs. The main difference is in the ballast ratio, which is a little higher, partly because the draft is less and the keel shape different. At the time, Bavaria had a reputation similar to some of the Scandinavian builders and the internal finish and fittings were generally high quality with more of a "craftsman" feel than later production line built boats. The basic construction is robust and equipment comes from well known manufacturers such as Selden, Lewmar, Raymarine etc. Many boats were sold to charter operators, particularly in Greece and Croatia where they have an excellent reputation.
As with any 25+ year old boat, it is important to consider the current condition and past maintenance. The engine is worth close inspection as the 2003T originally fitted is not one of Volvo's best efforts.
Sounds like a good choice for your intended use, particularly for a large crew. I remember chartering a similar (later) 42 with 6 people and appreciated the space. The extra side cabin is very useful.
